Extractive distillation operation for preparation of catalytic cracking feed stocks



Jan. 15, 1957 N. P. PEET 2,7 EXTRACTIVE DISTILLATION OPERATION FORPREPARATION OF CATALYTIC CRACKING FEED STOCKS Filed Dec. 10, 1954 FIG.2. 25 7532? g 3: i

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EXTRACTIVE DISTILLATION OPERATION FOR PREPARATION OF CATALYTIC CRACKINGFEED STOCKS Nick P. Peet, Baytown, Tex., assignor, by mesne assignments,to Esso Research and Engineering Company, Elizabeth, N. 3., acorporation of Delaware Application December 10, 1954, Serial No.474,477 14 Claims. (Cl. 196-49) This invention concerns a novel erativeto reduce the content present in catalytic cracking charge stocks. Theinvention concerns the use of a novel refluxing agent in a distillationoperation in a manner to cause removal of metal contaminants by theprinciples of extractive distillation. The novel refluxing agentemployed in accordance with this invention is a high molecular weightasphaltic material.

In recent times, a great deal of efiort has been applied in thepetroleum refining field to increase the recovery of catalytic crackingfeed stock from residual fractions of petroleum oil. Conventionally, thefeed stock to a catalytic cracking operation constitutes a so-called gasoil fraction of crude oil which boils in the range of about 400 to 800F. or somewhat higher. Portions of the gas oil boiling distillationprocess opof metal contaminants petroleum crude oil boiling above therange may be considered residual petroleum fractions. Such residualfractions may be used as sources of asphalt, fuel, and other productswhich are of relatively low economic value. It, therefore, becomesattractive to develop means for successfully utilizing portions of theresidual fractions of crude oil as catalytic cracking feed stock.

Attempts to employ heavier fractions of crude oil for catalytic crackinghave been limited heretofore due to the presence of certain metalcontaminants in such heavy fractions. Thus the highest boiling fractionsof a crude oil contain substantial portions of metal contaminants,particularly including nickel, vanadium and iron compounds. The residualfractions of typical crude oils generally contain these metalcontaminants in quantities of about 10 to 500 pounds per 1000 barrels ofresidual fraction. When an attempt is made to segregate higher boilingdistillate fractions of a crude oil, some portion of these metalcontaminants are inherently and unavoidably carried over into thedistillate products. For example, in a vacuum distillation operationwhere a heavy boiling gas .oil fraction is segregated from a crude oil,about 0.5 to 10 pounds per 1000 barrels of metal contaminants Will beobtained in the gas oil distillate in a typical situation. In thisexample, the gas oil distillate referred to would have a boiling rangeof about 700 to 1100 F.

The problem of metal contaminant carry over in the segregation of heavydistillate fractions is apparently due to two phenomena. First of all,it appears that the metal contaminants occur or are converted duringdistillation to the form of metal complexes. These complexes maygenerally be identified as large condensed ring substances. Some ofthese metal complexes and particularly nickel porphyrins aresufliciently volatile so as to be carried overhead at a temperature ofabout 1050 F. Consequently, when attempting to segregate heavy boilinggas oil fractions including components boiling above about 900 F.,volatile metal contaminants are unavoidably obtained in the distillateproduct. It

" nited States Patent 0 appears that a second phenomenon is alsoinvolved which may be referred to as mechanical entrainment. Togenerally indicate the mechanism of this effect, it can be consideredthat a small portion of high boiling liquid hydrocarbons from theresidual fraction are normally entrained overhead in a distillationoperation. Since such liquid hydrocarbons contain concentrated amountsof metal contaminants, such entrainment in distillate products accountsfor a portion of the metal contamination of such distillates.

By virtue of the fact that catalytic cracking operations are adverselyaffected by the presence of such metal contaminants, it is apparent thatthe need exists for some means to recover high boiling fractions of acrude oil while eliminating contamination in the manner described. Thepresence of metal contaminants and particularly nickel in a catalyticcracking operation results in direct contamination of the catalyst bythe metal compound. Metal continues to accumulate on the catalyst duringthe life of the catalyst having the result of seriously altering thecatalytic properties of the catalyst. In general, it is consideredessential to reduce the metal contaminant content of the catalyticcracking feed stock to a value of less than about 3 pounds per 1000barrels. It is the principal object of this invention to provide thisobjective in a novel and practically attractive manner.

The present invention is based on the discovery that certain highmolecular weight condensed ring aromatic compounds are effective assolvents for the objectionable metal complexes present in crude oil.Consequently, by introducing these particular solvents into adistillation zone, by virtue of their high boiling character, metalcontaminants can be removed from distillate fractions by the principlesof extractive distillation. The present invention, therefore, concerns atechnique by which certain high molecular weight condensed ring aromaticcompounds are employed as an extractive distillation refluxing agent inthe segregation of heavy oil fractions.

The extractive distillation refluxing agent to be employed may bedefined as a high molecular Weight asphaltic material containing a lowconcentration of nickel compounds and particularly characterized bysubstantially no volatilization of nickel components at temperatures ofabout 1050 to 1300" F. at atmospheric pressure. The high molecularweight asphaltic material referred to contains a large portion ofcondensed ring aromatic compounds believed to have more than about 15rings in the molecule. The asphaltic materials boil from about 1050" F.up to about 1400 F. and higher. For the purpose of this invention it isapparent that such refluxing agents must contain a low concentration ofmetal contaminants, although some high boiling metal contaminants can betolerated. In this connection, it is essential that the concentration ofmetal contaminants capable of volatilizing at temperatures below about1300 F. should be less than about 2 to 5 pounds per 1000 barrels. Insome cases, somewhat greater concentrations of higher boiling metalcontaminants can be tolerated, the limitation relating to thepossibility of entrainment in the particular distillation facilitiesavailable.

The extractive distillation refluxing agent can be derived from twopotential sources. First of all, in the case of those petroleum crudeoils having remarkably low content of total metal contaminants orremarkably low content of volatile metal contaminants, it is possible tosegregate suitably high molecular weight asphaltic material for thepurposes of t 's invention. This, however, is the exceptional case sincethe asphaltic materials of the character required when derived from theaverage or typical crude oil contain prohibitively high concentrationsof metal contaminants.

This does not prevent using heavy virgin stocks as refluxing agents. Forexample, very high molecular weight fractions obtained by solventprecipitation such as with a low molecular weight hydrocarbon, eventhough'containingappreciably amounts of metal contaminants are suitableagents because the initial boiling point of such fractions will usuallybe high enough to prevent volatilization of contaminants-at normalvacuum distillation temperatures up to about 1050 F.

The refluxing agent can also be a synthetic, high molecular weightasphaltic material derived from cracking operations. A desirable sourceof the refluxing agent free from metal contaminants is secured fromthermal tar obtained in conventional refinery operations, particularlywhen cracking distillate stocks. Such a tar may be obtained bydistilling the products from a thermal cracking unit. The objective isto remove the greatest possible portion of constituents boiling belowabout I050 F. This is best conducted by carrying out the distillation asa vacuum flashing process although alternatively a deasphalting processmay be used to segregate the desired asphaltic fraction.

While, as indicated, the refluxing agent to be employed can be derivedfrom virgin or thermally cracked stocks by distillation or deasphalting,the preferred source of the refluxing agent is from :catalyticallycracked products. The highest boiling fractions of catalytically crackedfeed stocks are conventionally designated as cycle oil and/ or clarifiedoil. Such fractions include high molecular weight condensed ringaromatic compounds which may be designated as synthetic asphalts formedduring the catalytic cracking operation. These materials areparticularly effective in the practice of this invention and can berecovered from cycle oil or a clarified oil by vacuum flashing ordeasphalting processes. It is also attractive to obtain the refluxingagent from thermal tars derived from catalytically cracked stock.

As used hereinafter the term synthetic asphaltic material will be usedto identify these extractive distillation refluxing agents of thisinvention.

In the practice of this invention, synthetic asphaltic materials areinjected into the distillation zone for segregating heavy boiling gasoil fractions in proportions of about 1% to 50% based on the hydrocarbonvapor rate at the portion of the distillation zone at which therefluxing agent is injected. The lower limit of the amount of refluxingagent to be used is determined by the concentration of metalcontaminants in the stock distilled coupled with a consideration of thedegree of contaminant removal required in the distillate product. Ingeneral, however, it is preferred to employ amounts of refluxing agentin the range of about 2% to about 20% and particularly about 5% based onthe hydrocarbon vapor rate in the distillation operation. In order tosecure the desired contaminant removal from heavy distillate products,it is essential that the refluxing agent be brought into thedistillation tower at a point somewhat below the side streamwithdrawalpoint of the highest boiling distillate product. The refluxingagent must be brought into intimate contact with upflowing hydrocarbonvapors in the distillation tower. For this purpose, the refluxing agentmust be deposited over at least one plate in the distillation tower andpreferably a greater number of plates ideally providing at least onetheoretical stage of contacting of the vapors. If desired, the refluxingagent together with extracted metal contaminants can be removed from thedistillation tower at a lower side stream withdrawal point or,alternatively, the refluxing agent can be withdrawn together With thebottoms product of the distillation tower.

Referring now to the accompanying drawings, preferred embodiments ofthis invention are diagrammatically illustrated in which:

Fig. 1 diagrammatically illustrates application of the present inventionto a vacuum distillation operation;

Fig. 2 shows the application ofthe invention in a coking process;

Fig. 3 shows the application of the invention to a combinationdistillation and cracking operation;

Fig. 4 illustrates the invention when employed in a combination cokingand cracking operation; and

Fig. 5 shows the invention when used in a combination distillationcoking and cracking operation.

Referring first to Fig. l, the invention is illustrated in its basicapplication to a distillation tower. In Fig. l the numeral I identifiiesa distillation tower for the segre gation of oil fractions of apetroleum crude oil. Tower 1 can particularly constitute a vacuum stilloperated at pressures of about 25 mm. to 250 mm. of mercury. Thus inconventional refinery operations a petroleum oil is generally subjectedto preliminary fractionation in an atmospheric distillation towerproviding a bottoms fraction constituting reduced crude oil boilingabove about 600 F. Such a reduced crude oil can be brought into tower 1through line 2 at temperatures of about 600 to 850 F. The reduced crudeoil undergoes a flashing operation in the lowest portion of the vacuumdistillation tower so that light portions of the reduced crude arecarried overhead in vaporform and the heaviest boiling fractions arecarried downwardly toward the bottom of the tower. The lightest boilingfractions can be removed from line 3 but successively higher boilingfractions can be removed from side stream withdrawals 4, 5 and 6.Ordinarily the heaviest fractions of the reduced crude are'subjected toa steam stripping operation in the bottom of the distillation towerutilizing steam injected through line 7. The stripped productsconstituting residual crude oil are then withdrawn through bottomswithdrawal 8.

It is an object of this invention to eliminate or substantially reducethe content of metal contaminants carried overhead in the higher boilingdistillate fractions such as those withdrawn through lines 5 and 6. Inthis connection, data are presented in Table I illustrating the amountof metal contaminants typically present in reduced crude derived from avariety of sources. In this table columns 1, 2, 3, 4 and 5,respectively, show the characteristics of residua derived from a mixtureof Gulf Coast and West Texas crudes, a West Texas crude, a Panhandlecrude, a Hawkins crude and a Lagunillas crude.

TABLE I T yptical feed stock inspections Percent on Crude 9.8 12.8 15. 629. 0 44.0 Gravity, API 8. 7 8. 7 20. 1 4. 7 (i. 5 Viscosity, SSU at 210F 679 Conradson Carbon, Wt. Perce 8. 17.3 8 40 19.8 24. 0 Bomb Sulfur,Wt. Percent 3.05 3. 67 t. 6 3.1 Contaminants, #/l,000 Bbls:

Ni l3. 0 9. 0 5. 0 10. 2 24. 3

In accordance with this invention, a synthetic asphaltic material of thecharacter identified is brought into distillation tower 1 through line 9at an introduction point somewhat below the lowest side streamwithdrawal point. The synthetic asphalt is introduced in quantities ofabout 1% to 50% by weight based on the volume of hydro carbon gasesflowing upwardly through the portion of the distillation tower at whichthe synthetic asphalt is introduced. Since the synthetic asphalt, asidentified, is a high boiling'material, it is present in liquid phase indistillation tower 1. Contact with upflowing hydrocarbon vapors resultsin selective extraction of metal contaminants and, in addition,the'synthetic asphalt serves to prevent entrainment of liquid portions"of the residual oil present in tower 1. By both of these mechanismscontact of the -asphaltic materials with upflowing vapors in thedistillationtower serves-to eliminate metal contamination of distillateproducts withdrawn from the tower. The synthetic asphaltic material canbe withdrawn from distillation tower 1 through lower side streamWithdrawal or, alternatively, the asphaltic material may be allowed topass downwardly through the tower for removal with residuum through line8. Preferably the synthetic asphaltic material containing extractedmetallic contaminants is then discarded from the system and finds use asa fuel. Optionally, however, on withdrawal from the tower the syntheticasphaltic material may be subjected to severe flashing conditions,permitting removal of high boiling gas oil rich in metal contaminants asoverhead product and withdrawal of a purified synthetic asphalticmaterial as a bottoms product which can be recycled to tower 1.

The remaining figures of the drawings diagrammatically illustrateapplication of the principles of Fig. 1 in a variety of refiningoperations. These will be briefly identified with the understanding thatthe basic individual processes involved are conventional and well knownto the art.

With reference to Fig. 2, for example, the invention is illustrated asapplied to the distillation of products subjected to a coking operationin order to obtain heavy boiling products suitable for catalyticcracking. In the drawing, the numeral designates a coking reactor inwhich residual portions of petroleum oil are contacted with cokeparticles at temperatures of about 800 to 1000 F. in order to secureconversion to lighter boiling constituents. The coking operationconducted in zone 2% may be of any desired type and can constitue, forexample, a fluidized operation in which coke particles are maintained asa fluid bed in accordance with the principles of fluidized solidscontacting. Residual oil introduced into coking zone 20 through line 21undergoes conversion permitting removal of a product stream through line22 including gases, intermediate liquid fractions, and unconvertedresidual fractions. Coke can be withdrawn periodically from zone 20through line 23. The products of the coking process removed through line22 are then introduced to a distillation zone 24. The distillation maybe either atmospheric or vacuum distillation but preferably constitutesvacuum distillation of the character referred to in connection withFig. 1. successively higher boiling portions of the feed are removedfrom still 24 through lines 25, 26,. 27 and 28. Uncoverted portions ofthe residual stock originally fed to the coking process can be removedas a bottoms product through line 29 and can be recycled to the process.

In accordance with this invention, a synthetic asphaltic material isintroduced to distillation zone 24 through line 30 at a point somewhatbelow the side stream withdrawal of the highest boiling distillateproduct. This distillate product will include heavy gas oil suitable forcatalytic cracking. As indicated in connection with Fig. 1, the injectedsynthetic asphaltic material can be removed from the tower 24 through alower side stream Withdrawal 31 or, alternatively, the asphalticmaterial may be permitted to remain in the bottoms product of thefractionator.

The process of Fig. 2 is a particularly valuable process for upgradingresidual stocks to catalytic cracking feed material. The coking step ofthe process serves to remove a-substantial portion of metal contaminantsthe coking feed stock. These metal contaminants are deposited on thecoke solids employed and/or produced in the process; consequently, byusing the process of this invention in combination with this effect,heavy gas oil feed stocks having extremely low content of metalcontaminants can be obtained for catalytic cracking feed stoc Fig. 3fllustrates the application of this invention to a fractionator of thecharacter employed in the so-called combination distillation crackingoperation. As illustrated by Fig. 3, fractionation of catalyticallycracked products can be carried out in the same distillation tower inwhich a crude oil is fractionated. Thus the terial can be removed from alower total product from catalytic reactor "18 may bepassed through line32 for introduction near the bottom portion of the fractionator 33.Crude oil is brought into fractionator 33 at an intermediate portion ofthe tower through line 34. Light boiling fractions of the catalyticcracking products rise upwardly in vapor form through the distillationzone, serving as an effective stripping agent for heavy portions of thecrude oil. In addition, other stripping gases may be brought into tower33 through other side stream introduction points. Such stripping agentscan constitute light naphtha fractions derived from other refiningprocesses, such as a reforming process. The necessary heat input for thedistillation operation is supplied by a reboiler circuit indicated bynumeral 36. Distillate products including fractions of both the crudeoil and the catalytically cracked products are withdrawn from the towerthrough lines 37, 28, 39 and 49. Operation of still 33 can be adjustedso that the product withdrawn through line 40 will constitute a gas oilsuitable for catalytic cracking. In accordauce with this invention thedistillate products are processed to minimize the presence of metalcontaminants by introduction of a synthetic asphaltic material of thecharacter described through line 41. This mapoint in the tower throughline 42 after contact with upflowing vapors or, alternatively, thesynthetic asphaltic material may be permitted to pass downwardly throughthe tower for re moval with residual oil through line 43.

The process of Fig. 3 is particularly attractive in providing adistillation process for segregating a heavy gas oil for catalyticcracking which can be conducted at atmospheric pressures. The use ofthis invention as described in this figure is particularly attractive inproviding heavy boiling gas oils of low metal content suitable forcatalytic cracking.

With reference to Fig. 4, this figure diagrammaticallyillustratesapplication of the invention to the distillation of theproducts of a coking operation when con-. ducted in combination with acracking reaction. In this drawing a high boiling residual fraction ofcrude oil containing metal contaminants is introduced to a cokingreactor 45 through line 46. The coking process may be of the characteridentified in connection with Fig. 2. The hydrocarbon products. of thecoking process are removed through line 47 for introduction to asembbing tower 48 which is essentially a distillation zone in which thetotal coke products which have been converted during coking are removedoverhead through line 49. These products are then subjected to catalyticcracking reactor 50. The products of catalytic cracking are then passedthrough line 5-1 to distillation tower 52. Still 52 is preferably avacuum distillation tower permitting segregation of light boilingproducts through lines 53, 54, 55 and 56 and segregation of a heavycatalytic tar through line 57. This tar will constitute a syntheticasphaltic material which can be recycled through line 57 to scrubbingtower 48 for contact with the coke products. Portions of the residualstock originally fed to the coking zone together with the syntheticasphaltic material are removed from scrubbing tower 48 through line 58for recycle to the coking operation.

As described, therefore, Fig. 4 illustrates a process having theadvantages of Fig. 2 by employing a combination of coking, catalyticcracking and fractionation. The process of Fig. 4 provides an integratedprocess for production of a suitable extractive distillation refluxingagent and use of this agent to effectively upgrade residual stock forcatalytic cracking.

Fig. 5 illustrates a somewhat different combination of distillation,coking and cracking. Fractionation zone 66 of Fig. 5 is similar tofractionation zone 33 of Fig. 3: and constitutes a combinationfractionator in which both crude oil and products of catalytic crackingare subjected to fractionation. in the samedietillationzone.

illustrated in Fig. 5, a crude oil isintroduced' into distillation zone60 through line 61 together with the total products of a catalyticcracking zone brought into the tower through line 62. Distillateproducts of varying boiling ranges are withdrawn from tower 60 throughWithdrawal lines 31, 82, 83, 84 and 85. As described in connection withFig. 3 the product of line 85 may constitute a gas oil fractionadaptable for catalytic cracking. In order that this gas oil fraction befreed of metallic contaminants present in the crude oil brought intodistillation zone 60, synthetic asphaltic material is brought into tower60 through line 66. Residual fractions are removed from distillationzone 60 through line 67 together'with the synthetic asphaltic materialintroduced to the tower. These are subjected to a coking operation inthe coking reactor 68. Products of the coking reaction are@passedthrough line 69 to a scrubber 7 3' of thecharacter described inconnection with Fig. 4. in scrubbing tower 70, the coking products arecontacted with a synthetic asphaltic material introduced through line71. The lighter boiling products are removed from tower 70 through line72for introduction to the catalytic cracking zone 73 together with thegas oil in line 85 derived from still 60. Residual products of scrubbingtower 70 are returned to the coking reactor through line 75.

It will be observed that the process of Fig. 5 provides a combination ofthe processes of Figs. 2, 3 and 4 which provides an attractiveapplication for the present invention. A particular feature of theprocess of Fig. 5 is the manner in which a high molecular weightasphaltic material is essentially used in a two-stage contactingoperation to eliminate metal contaminant content of a catalytic crackingfeed. This occurs in combination with the elimination of metalcontaminants achieved in a coking operation so the process is welladapted for providing the highest quality catalytic cracking feed stock.

It will be observed from the description of this invention, as broughtout in connection with the drawings, that the present invention is ofbroad application to the recovery of high boiling. distillate fractionsintended for catalytic cracking. The process of this invention may beadapted to virtually any type of distillation operation including theatmospheric, vacuum, and stripping type distillation operationsparticularly described. Included within the scope of this invention isthe new combination of coking and catalytic cracking processes withfractionation so as to employ the full advantages of this invention.

What is claimed is:

1. In a distillation process wherein a metals contaminated petroleumhydrocarbon feed stock containing a substantial portion of hydrocarbonconstituents boiling above 900 F. is charged to a distillation tower andfractionated therein to segregate at least a heavy gas oil distillatefraction including said constituents boiling above 900 F., theimprovement which comprises countercurrently contacting saidconstituents boiling above 906 F. in vapor phase in said tower prior towithdrawal of the same under extractive distillation conditions with arefluxing agent introduced into said tower below the point of withdrawalof the heaviest distillate fraction, said refluxing agent comprising anextraneously derived high molecular weight asphaltic materialsubstantially free from metal contaminants, whereby a heavy gas oilfraction having a significantly reduced content of metal contaminants isobtained.

2. The process defined by claim 1 in which the said feed stockconstitutes a residual portion of petroleum oil characterized byinclusion of metal contaminants in amounts greater than at least 3pounds per 1000 barrels.

3. The process defined by claim 1 in which the said high molecularweight asphaltic material is introduced in amounts of about 1% to 50% byweight based onvaporous hydrocarbons present in the,- distillationprocess for contact with the asphaltic material.

4. The process defined by'claiml in which the said asphaltic material issynthetically derived from a cracking operation.

5. The process defined by claim l in which the said asphaltic materialconstitutes a tar derived from catalytic cycle stock and characterizedby inclusion of less than about 5 pounds per 1000 barrels of metalcontaminants.

6. In a distillation process wherein a metals con taminated reducedcrude oil boiling above about 600 F. and containing a substantialportion of hydrocarbon constituents boiling above 900 F. is charged to adistillation tower and fractionated therein to segregate a heavy gas oildistillate fraction including said constituents boiling above 900 F, theimprovement which comprises couutercurrently contacting saidconstituents boiling above 900 F. in vapor phase in said tower prior towithdrawal of the same under extractive distillation conditions with arefluxing agent introduced into said tower below the point of withdrawalof the heaviest distillate fraction, said refluxing agent comprising anextraneously derived high molecular weight asphaltic materialsubstantially free from metal contaminants, whereby a heavy gas oilfraction having a significantly reduced content of metal contaminants isobtained.

7. A process as in claim 6 wherein the distillation process is a vacuumdistillation process.

-8. A process as in claim 6 wherein the distillation process is anatmospheric distillation process.

9. A process as in claim 6 wherein the distillation process is a highpressure distillation-stripping process.

10. In a distillation process wherein the products of a coking processare charged to a distillation tower and fractionated therein tosegregate a heavy gas oil distillate fraction, the improvement whichcomprises countercurrently contacting the constituents of said heavy gasoil fraction in vapor phase in said tower prior to withdrawal of thesame under extractive distillation conditions with a refluxing agentintroduced into said tower below the point of withdrawal of the heaviestdistillate fraction, said refluxing agent comprising an extraneouslyderived high molecular weight asphaltic material substantially free frommetal contaminants, whereby a heavy gas oil fraction having asignificantly reduced content of metal contaminants is obtained.

11. In a distillate process wherein a feed stock comprising catalyticcracking products and a petroleum crude oil is charged to a distillationtower and fractionated therein to segregate a heavy gas oil distillatefraction including constituents boiling above 900 F., the improvementwhich comprises countercurrently contacting the constituents of saidheavy gas oil fraction in vapor phase in said tower prior to withdrawalof the same under extractive distillation conditions with a refluxingagent introduced into said tower below the point of withdrawal of theheaviest distillate fraction, said refluxing agent comprising anextraneously derived high molecular weight asphaltic materialsubstantially free from metal contaminants, whereby a heavy gas oilfraction having a significantly reduced content of metal contaminants isobtained.

12. In a process wherein a product obtained from the coking of aresidual petroleum hydrocarbon fraction is passed upwardly through ascrubbing tower and thence to a catalytic cracking process as the feedstock therefor, and wherein the products from the catalytic crackingprocess are fractionally distilled to provide a residue containing asynthetic high molecular weight asphaltic material substantially freefrom metal contaminants, the improvement which comprisescountercurrently contacting said coking product with said residue insaid scrubbing towe'r'prior to removal of said coking product from saidscrubbing tower.

13. In a combination process wherein the products of a catalyticcracking operation and a petroleum crude oil are charged to adistillation tower andfraction'ated therein to provide a heavy gas oildistillate fraction and a residual fraction, wherein the said heavy gasoil distillate fraction is charged to the said catalytic crackingoperation as a portion of the feed therefor, wherein the said residualfraction is subjected to a coking reaction and wherein the products ofthe said coking reaction are passed upwardly through a scrubbing towerand are then charged to the said catalytic cracking operation as anotherportion of the feed therefor, the improvement which comprisescouutercurrently scrubbing said coking products with an extraneouslyderived high molecular weight asphaltic material substantially free frommetal contaminants prior to removal of said coking products from saidscrubbing tower, and also countercurrently contacting said heavy gas oildistillate fraction in said tower in vapor phase prior to removal of thesame under extractive distillation conditions with a refluxing agentintroduced into said tower below the point of withdrawal of the heaviestdistillate fraction, said refluxing agent comprising an extraneouslyderived high molecular weight asphaltic material substantially free frommetal contaminants.

14. In a distillation process wherein a petroleum hydrocarbon residualfraction containing from about to 500 pounds per 1000 barrels of metalcontaminants is charged to a distillation tower and fractionated thereinto i provide at least a between about 700 gas oil distillate boiling inthe range and about 1100 F., the improvement which comprisescountercurrently contacting said distillate fraction in ascending vaporsphase in said tower prior to withdrawal of the same under extractivedistillation conditions with about 1 to about based on the ascendingvapors of tion, of a refluxing agent introduced weight percent, saiddistillate fraclow the point of withdrawal of the heaviest distillatefraction, said refluxing agent boiling in the'range between about 1050and about 1400 F. and comprising an extraneously derived high molecularweight asphaltic material substantially free from metal contaminants.

References Cited in the file of this patent UNITED STATES PATENTS intosaid tower be- I

1. IN A DISTILLATION PROCESS WHEREIN A METALS CONTAMINATED PETROLIEUMHYDROCARBON FEED STOCK CONTAINING A SUBSTANTIAL PORTION OF HYDROCARBONCONSTITUENTS BOILING ABOVE 900*F. IS CHARGED TO A DISTILLATION TOWER ANDFRACTIONATED THEREIN TO SEGREGATE AT LEAST A HEAVY GAS OIL DISTILLATEFRACTION INCLUDING SAID CONSTITUENTS BOILING ABOVE 900*F., THEIMPROVEMENT WHICH COMPRISES COUNTERCURRENTLY CONTACTING SAIDCONSTITUENTS BOILING ABOVE 900* F. IN VAPOR PHASE IN SAID TOWER PRIOR TOWITHDRAWAL OF THE SAME UNDER EXTRACTIVE DISTILLATION CONDITIONS WITH AREFLUXING AGENT INTRODUCED INTO SAID TOWER BELOW THE POINT OF WITHDRAWALOF THE HEAVIEST DISTILLATE FRACTION, SAID REFLUXING AGENT COMPRISING ANEXTRANEOUSLY DERIVED HIGH MOLECULAR WEIGHT ASPHALTIC MATERIALSUBSTANTIALLY FREE FROM METAL CONTAMINMANTS, WHEREBY A HEAVY GAS OILFRACTION HAVING A SIGNIFICANTLY REDUCED CONTENT OF METAL CONTAMINANTS ISOBTAINED.